The present invention relates to an injection mold for insert-molding a synthetic material around the edge of a filter material used particularly for the filtration of air streaming into the interior of a motor vehicle. Further, the invention relates to a method for producing a filter for the filtration of fluids, as used particularly in vehicles. Finally, the invention relates to a filter for the filtration of fluids.
For improving the function of filters for the cleaning of a fluid flow, i.e. particularly of an air flow, increasing use is made of active carbon filters, apart from conventional particle filters. For easy handling during-the production of such filters, it is suitable to use filter materials which, in addition to at least one particle filter layer, also comprise an active carbon layer of active carbon particles. For improved convenience during the assembly of filters, the filter materials of the filters are connectedxe2x80x94at least along parts of their edgesxe2x80x94to stiffening elements which are particularly provided as frames surrounding the edge of the filter material. Such frames or stiffening elements fulfill a holding function because, if the filter material is folded into a zig-zag shape for enlarging the filter surface, they will maintain the corrugated structure of the filter surface.
The attachment of stiffening elements or a continuous frame to a filter material is realized in a cost-saving manner by molding a synthetic material around the filter material. For this purpose, the filter material is inserted into an injection mold, with the edge of the filter material projecting into a molding space of the injection mold and the rest of the filter material being arranged in a receiving space of the injection mold. Now, to prevent the leakage of synthetic material into the receiving space when injecting the synthetic material into the receiving space, the injection mold must be in sealing abutment on the filter material so that no fluid connection between the molding space and the receiving space exists for the viscous synthetic material. The molding of synthetic material around a filter material is difficult particularly if, due to the structure of the filter material, a tightly sealed closure between the molding space and the receiving space can be realized not at all or only by extreme pressure forces acting on the filter material. This is the case, e.g., when the filter material, in addition to a particle filter layer, also comprises an active carbon layer of active carbon particles or has porous properties. The porous structure of an active carbon layer requires the application of relatively high press-on forces which, in the region between the molding space and the receiving space, are exerted by the injection mold onto the filter material to thus squeeze off the filter material, as it were. These high force cause considerable wear of the injection mold so that the cost-saving effects obtainable by the molding technology are partially neutralized due to increased expenses for injection molds.
It is an object of the invention to provide an injection mold for insert-molding a synthetic material around the edge of a filter material comprising at least one particle filter layer and at least one active carbon layer of active carbon particles, wherein the region between the molding space and the receiving space is tightly sealed against leakage of the viscous synthetic material in the direction towards the filter material, with only minimum press-on forces being required.
For solving the above object, the instant invention provides an injection mold for insert-molding a synthetic material around the edge of a filter material. In particular, the filter material comprises at least one particle filter layer and at least one active carbon layer of active carbon particles. The injection mold comprises a first mold half and a second mold half, having mutually confronting mold walls. In the assembled state the two mold halves define the following cavities therebetween a receiving space for the filter material; a molding space for accommodating the edge of the filter material and for forming the synthetic material to be molded around the edge of the filter material; at least one injection channel entering the molding space; and a transition space arranged between the receiving space and the molding space for accommodating the edge portion of the filter material adjacent the edge of the filter material. The transition space is formed with a constricted portion for preventing the leakage of synthetic material from the molding space into the receiving space. The constricted portion comprises at least two narrowed portions with a widened portion arranged therebetween. The distance of the mold walls of the two mold halves is smaller in the narrowed portions than in the widened portion, and the two narrowed portions and the widened portion are arranged respectively transverse to the direction of the transition space, which is oriented between the molding space and the receiving space.
The injection mold of the invention comprises two mold halves which, in the closed condition, form a receiving space for the filter material, a molding space for forming the synthetic material to be molded around the edge of the filter material, and a transition space between the receiving space and the molding space. The filter material to be subjected to insert molding is placed into the receiving space, with the edge portion of the filter material extending through the transition space up to the molding space. Thus, the actual edge of the filter material projects from the transition space into the molding space. Arranged within the transition space is a constricted portion formed by the walls of the two mold halves; within this constricted portion, the mold walls of the mold halves are arranged in fluid-tight abutment on the filter material when the latter has been inserted.
According to the invention, the constricted portion of the transition space comprises at least two narrowed portions and a widened portion arranged therebetween. In each of the narrowed portions, the distance of the mold walls of the two mold halves is smaller than in the widened portion. In this manner, the two mold halves together with the inserted filter material provide a fluid-tight closure, formed in the manner of a labyrinth seal, against the synthetic material injected in a liquid state. The at least two narrowed portions, which are arranged transversely to that direction of the transition space which is oriented between the molding space and the receiving space and, when viewed along the direction of the transition space are arranged behind each other between the molding space and the receiving space, act like two barriers for preventing the intrusion of viscous synthetic material from the molding space into the receiving space.
Because of the provision of a plurality of narrowed portions, the two mold halves in these narrowed portions need abut the filter material only with a lower press-on force to realize a fluid-tight closure between the molding space and the receiving space. The widened portion arranged between respectively two narrowed portions serves for accommodating filter material which has been laterally displaced due to squeezing in the narrowed portions. Thus, in the invention, active carbon particles (in as far as they are not decreased in size when squeezing the filter material) are urged from the edge zones of two adjacent narrowed portions into the widened portion arranged therebetween. Further, the widened portion or each of the plurality of widened portions functions like a dead volume for receiving viscous synthetic material which, during the molding process performed on the edge of the filter material (possibly still) passes through the narrowed portion on the side of the molding space.
Preferably, a highly reliable production with an almost negligible percentage of rejects is realized by providing the constricted portion of the transition space with three narrowed portions with intermediate widened portions, with the narrowed portions and the widened portions being arranged alternately in that direction of the transition space which is oriented between the molding space and the receiving space.
In a further preferred embodiment of the invention, also the molding space is provided with at least one constricted portion dividing the molding space into a first partial space and a second partial space. This constricted portion of the molding space increases the flow resistance to the injected synthetic material. The edge of the filter material projects into that partial space of the molding space which follows the transition space, and the injection channel or the injection channels for injecting the synthetic material into the molding space enter into the other partial space of the molding space. By this arrangement, a flow gradient directed to the edge of the filter material is generated within the molding space. As a result, it can be safeguarded within in certain limitsxe2x80x94that, when injecting the synthetic material, that partial space of the molding space which has the injection channels entering thereinto will be filled first. Only thereafter, the front of the viscous synthetic material passes the constricted portion to enter the other partial space of the molding space which has the edge of the filter material projecting thereinto. Thereby, in turn, it is accomplished that the synthetic material will primarily flow from the partial space comprising the injection channels into the partial space receiving the edge of the filter material, instead of flowing in the reverse direction. In this manner, a xe2x80x9cwashing outxe2x80x9d of the edge of the filter material, i.e. a detachment of active carbon particles from the edge of the filter material, is largely prevented, which has a favorable effect for the design of the finished filter because no or nearly no active carbon particles will penetrate into the synthetic-material element molded around the filter material. The injection mold of the invention is particularly suited for insert molding a synthetic material around filter materials which comprise an active carbon layer of active carbon particles arranged between two nonwoven layers. In such a configuration, one of the two nonwoven layers functions as a particle filter layer and is preferably formed from an electret material. This electret material preferably comprises synthetic fibers of polypropylene which have been given electret properties. While that layer of the filter material which serves as a particle filter layer is arranged before the active carbon layer when viewed in the flow direction, the second nonwoven layer is arranged behind the active carbon layer and is particularly provided to keep the active carbon particles from being detached and carried along with the fluid flow to be filtered.
The inventive filter is provided with a synthetic material therearound by an insert molding process using the inventive injection mold. The filter comprises a filter material having upper and lower sides and a limiting edge. In particular the filter material comprising at least one particle filter layer and an active carbon layer of active carbon particles with a frame surrounding the limiting edge and having the limiting edge of the filter material embedded therein. At least two deepened grooves having a rib arranged therebetween and are arranged adjacent to the frame and substantially parallel to the direction of the frame at least in a part of the upper side and/or the lower side of the filter material.
The inventive filter is distinguished particularly by the provision of two deepened grooves in the frame-side region of the filter material, with a rib formed between the two deepened grooves. The at least two deepened grooves and the rib arranged therebetween are arranged substantially in parallel to the direction of at least one portion of the (synthetic) frame (attached by insert molding).
Corresponding to the number of narrowed portions within the constricted portion of the transition space of the injection mold, the filter in the frame-side region of its filter material comprises a plurality of deepened grooves with respective ribs arranged therebetween.
In a preferred embodiment of the inventive filter, the frame has a reduced thickness in the region of the embedded edge of the filter material. This narrowed portion of the frame corresponds to the narrowed portion of the molding space of the injection mold that has been used for producing the inventive filter.